The old city area of the Castello Hill was used by the Romans and other earlier inhabitants of Cagliari, but it was the Pisans that transformed it into the medieval town that remains today. This is home to the Sardinian Archaeological Museum, which is home to several collections of pre-Classical art and artifacts, including those dating to the prehistoric Nuragic civilization.

The area around Cagliari, whose name actually means Castle, is home to several fortifications and medieval era castles. Among these is the Castle of St. Michele, which today is only a shadow of its former glory. Now mostly in ruins, the castle was built during the Pisan Rule of the 12th century, on what is believe to have been the site of an early monastery, and this could explain the holy name that it was given. This fortification was further strengthened during the rule by the Kingdom of Aragon, when it served to protect the town. The remains of the Fortress of St. Ignazio, which once had guarded a very strategic point and thus provides some amazing views of Cagliari, today also look like a shell of what was a mighty citadel. Built during the Piedmont rule of the late 18 th century, the fortress was used to defend off the French invasion of the early 19th century.